Why the universe is not a black hole (merged)

The Big Bang Theory has the whole universe expanding from an initial size considerably smaller than an atoms nucleus. The universe at this stage must have all been inside a black hole with an event horizon radius of many light -years.

How is it that now the universe is much bigger than the size of the original event horizon - it has effectively escaped from a black hole - or is there still an event horizon out there somewhere at the edge of the universe?

Why did the universe not collapse and form a black hole at the beginning?

Since I think this is the main question, I'll take the liberty of quoting this section of the FAQ, to motivate people who are interested to read the entire document:

Sometimes people find it hard to understand why the big bang is not a black hole. After all, the density of matter in the first fraction of a second was much higher than that found in any star, and dense matter is supposed to curve space-time strongly. At sufficient density there must be matter contained within a region smaller than the Schwarzschild radius for its mass. Nevertheless, the big bang manages to avoid being trapped inside a black hole of its own making and paradoxically the space near the singularity is actually flat rather than curving tightly. How can this be?

The short answer is that the big bang gets away with it because it is expanding rapidly near the beginning and the rate of expansion is slowing down. Space can be flat while space-time is not. The curvature can come from the temporal parts of the space-time metric which measures the deceleration of the expansion of the universe. So the total curvature of space-time is related to the density of matter but there is a contribution to curvature from the expansion as well as from any curvature of space. The Schwarzschild solution of the gravitational equations is static and demonstrates the limits placed on a static spherical body before it must collapse to a black hole. The Schwarzschild limit does not apply to rapidly expanding matter.

If at one point, the entire universe as we know it, was confined to a volume smaller than that of an atom,..

do you have a link to something I could see that supports that?
I'm curious where that idea comes from. The technical papers I see coming out these days tell a slightly different story.

More like: "We suspect that General Relativity breaks down and fails to apply in situations of very high density pressure, curvature... However if GR DID apply then it would say the observable universe was once confined in a very small volume...etc..."

these are videos of some of the latest work on curing the bigbang singularity.
It is a gilt-edge elite workshop at one of the US top institutes of theoretical physics
Why not get your money's worth?, becauseif you are US taxpayer like me then your money went to NSF to pay for this elite workshop from Jan 8-26 this year
with people from Europe and all over and top US people
the whole thing basically motivated by the fact that the experts do not believe
that GR applies at very high density
they think that at very high density there are QUANTUM CORRECTIONS
(that could even e.g. make gravity a repulsive force at extreme density)
and a lot of experts, which you see here at the workshop, are groping for theoretical framework that will tell them
what the quantum corrections might be and that also could be tested in less extreme situations, and shown up if wrong.

But you can watch Gary Horowitz do his thing (he laughs a bit too much), or Ted Jacobsen, or whoever. It doesnt matter.

One possible answer to your question "why didnt it all collapse to hole?"
is that the whole "singularity" scenario is based on classic 1915 GR and it is widely suspected GR does not apply
and so people are working on various modifications and quantum corrections
where the game is to have a framework that you can TEST with what you can observe, like the CMB and solar system stuff, and galaxy-count structure formation stats, but that also says something about things you can NOT observe.

there are other explanations why it didnt collapse to hole, but I am saying first off to doubt the classical scenario.
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Here Pervect refers to the FAQ at John Baez website to explain just using basic stuff like Heisenberg uncertainty
and the fact that Schwarzschild BH solution is a static solution. That solution is excellent.
But it doesnt mention the huge ferment going on around quantum corrections to the theory of General Relativity
which is ultimately aimed at getting at what REALLY HAPPENED around the time expansion began. there is some new physics brewing which
I think its good to know about.

Presumably the non-application of the Schwartzchild radius to rapidly expanding matter also applies the other way round?

Suppose we organised 1/2 the matter in the universe to converge on a point in space with no prior black hole, then if the material is approaching fast enough it will reach the centre before a black hole event horizon forms ?

As for where I heard that "...at one point, the entire universe as we know it, was confined to a volume smaller than that of an atom,.."

Mostly I've read, almost offhand comments to that effect, in places like NY Times articles, articles on MSNBC.com, etc., where you'll get one line that will say something along those lines, as part of the background to explaining something else.

That point, when made, is rarely, if ever, attributed to a source (which is why I wanted to ask about it in here, reporters often find themselves trying to explain something they don't quite understand themselves in science articles, so -- go fact check with a better source says me).

Anyway, THANKS FOR THOSE LINKS! I'm dyin' to go watch, listen, and read about this.

Suppose we organised 1/2 the matter in the universe to converge on a point in space with no prior black hole, then if the material is approaching fast enough it will reach the centre before a black hole event horizon forms ?

Not knowing a great deal i was wondering if that is what they would call a naked singularity.

Not knowing a great deal i was wondering if that is what they would call a naked singularity.

Are naked singularities possible.

The cosmic censorship hypothesis suggests that naked singularities are not possible, but I don't think this has been proven.

Naked singularities are singularities without an event horizon, and aren't related to the original question. One way that naked singuarities could arise is by a black hole spinning above a certain critical rate. It can be shown that a black hole cannot be "spun up" from an ordinary black hole into a naked singularity, but as far as I know the question of whether naked singularities can form out of collapsing matter is somewhat open (the cosmic censorship hypothesis is still a hypothesis).

I can't really answer Roy's original question cited by umicky above, unfortunately. It's a bit too detailed, and would involve many finicky details to answer, such as:

Do we use the absolute horizon or apparent horizon? How do you definie simultaneity between the event in the center and the horizon, (simultaneity is relative)? What's the exact distribution of matter?